Determining geological facies in a given field is useful in the context of exploration for an exploitation of high hydrocarbons or gas since this makes it possible best to estimate the available resources and consequently the economic value of the field.
In addition, this determination makes it possible to establish fine models concerning the future production of the fuel according the well parameters.
There thus exist a large number of techniques for establishing facies models using, for example:                drillings,        seismic images,        karstic simulations,        geostatic simulations,        conceptual knowledge of geologists (e.g. facies gradient in a direction in space),        etc.        
These techniques may be combined in order to obtain more precise results.
These techniques make it possible to establish qualitative and/or quantitative models.
A quantitative model is a model, for example meshed, where the meshes provide a facies proportion for each of these meshes. A qualitative model is a model, for example meshed, where the meshes provide a trend for each facies: for example, these meshes make it possible to represent the major architectural elements (i.e. to display general or spatial aspects).
Facies models modelling n facies often consist of n proportion cubes, each cube being associated with a facies. For a mesh of the model, the sum of the proportions of the various facies (indicated by a corresponding mesh of their associated proportion cube) is equal to 1.
In order to benefit from the information from various qualitative or quantitative models (in general from 2 models), some methods have been proposed for combining these in a single final proportion model (or combined model).
Since the proportions of the final model may have an influence on the calculation of the hydrocarbon or gas resources, these proportions are followed attentively by geologists.
These methods are for example methods of combining models by minimising variants or methods proposed by commercial tools such as Petrel or by universities.
However, such methods are not free from faults.
For example, these methods in general provide only one solution. In addition, it is not possible to check the resulting proportions in the final model. Usually, the proportions of the final cube are calculated from the proportions of the initial cubes.
Furthermore, it is impossible to “apportion” the information provided by the various models and thus to “penalise” some models where the confidence index evaluated by geologists, geophysicists and/or well engineers is for example lower.
There is thus a need for a more flexible model combination method making it possible to check the resulting proportions, these proportions being able to be known very precisely by means of well data recorded on site.